Helping a friend

Hi Everyone,
A friend at work is interested in starting a new tank, He will be getting a 10-gallon, I already have his sponges and bio-max "curing" in my 38-gallon, been there about a week. I have a lot more fish in my tank that he will have. Will about a week and a half be long enough? I have suggested 3 female bettas and 3 cories to him. Does this sound ok?? or should he get 2 bettas and 2 cories to start off with? I have given him this site to read up and learn all he wants to know, and I work with him, so will be availble to help him also.
His sponges and bio are in a mesh bag floating in my tank, not running in my filter, I should have made that more clear.
Thanks for your time

Thank you for your responses! I was fortunate to add 3 females, 1 at a time, with no problems at all..they get along with each other and all the other fishies.